gcc8 is now minimum required compiler

    * docs/src/getting_started.adoc:

docs/src/getting_started.adoc

@@ -146,7 +146,7 @@ Comparing IDL to {cpp} with IDL to
 
 *AXCIOMA* has been tested with the following compilers
 
-* GCC version 4.8 or newer
+* GCC version 8 or newer
 * Microsoft Visual Studio 2015
 * Microsoft Visual Studio 2017
 * Microsoft Visual Studio 2019
@@ -157,7 +157,7 @@ Comparing IDL to {cpp} with IDL to
 
 *AXCIOMA* is currently actively supported on
 
-* RHEL 7.5 x86_64 using GCC 4.8.5
+* RHEL 8.0 x86_64 using GCC 8.2.1
 
 *AXCIOMA* is using at least the following {cxx11} features
 
@@ -183,10 +183,9 @@ prerequisites:
 |Prerequisite |Package name
 |ruby 2.0 or newer|ruby
 |perl version 5.10 or newer |perl
-|gcc version 4.7 or newer |gcc
-|g++ version 4.7 or newer |gcc-c++
+|gcc version 8 or newer |gcc
+|g++ version 8 or newer |gcc-c++
 |xerces-c++ version 3.0 or newer |xerces-c
-|clang 5 or newer |clang
 |GNU make version 3.81 or newer |make
 |GNU Bash|bash
 |=========================================